Thanks everyone for your ideas and suggestions. I used "Fix problems using Windows Update", where all apps, files and settings are preserved. It took 20 minutes and is all now back to normal. Yippee!!
Windows 11 File Explorer only previews PDF files in file preview pane as thumbnails.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(92.8, 60%, 18%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EGB%3C/text%3E%3C/svg%3E)
Greg Barnes
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Reputation points
Windows for home | Windows 11 | Files, folders, and storage
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(182.40000000000003, 36%, 27%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EPG%3C/text%3E%3C/svg%3E)
Paulo GM 63,950 Reputation points Independent Advisor2026-03-27T02:50:40.6733333+00:00 I understand that this change disrupts user workflow as many users have experienced the same problem. However, there are still ways to restore its function. You may refer to my answer on this thread for steps and see if it helps.
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Paulo GM 63,950 Reputation points Independent Advisor
2026-03-27T03:50:41.78+00:00 That's great! I'm glad you were able to fix it using the recovery option.
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Paulo GM 63,950 Reputation points Independent Advisor
2026-03-26T10:05:47.2466667+00:00 It is an app that supports the preview of the document. To know if you have set it properly, you can just right-click on the PDF file, then choose Properties > click on Change and set it to Edge (if you do not have a third-party app for your PDF files). Once you set your default app for the file, it should provide the preview for your file. But, as I mentioned earlier, if it doesn't work, then it is likely due to the security update on previewing a file.
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Greg Barnes 0 Reputation points
2026-03-27T00:56:01.87+00:00 This did not work. I tried every available PDF viewer in the list wit no change. Super frustrating. All the PDF files are my own that I created and are safe to view. I think MS has overstepped their power by interfering with my PC which was working perfectly until recently. I still only see the large thumbnails! Disgusting really, I relied on these previews and now my workflow is a mess. All because of a simple thing like previewing PDF my own (safe) PDF files. Does a Mac OS have a PDF file preview, because I need it.
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Paulo GM 63,950 Reputation points Independent Advisor
2026-03-26T02:34:00.37+00:00 Hi,
Right-click on the file then select Properties. If "Unblock" is available, select it and see if it fixes the problem. If not, we can take a look if the preview handler is correct and working. If that still doesn't work, I believe it has something to do with security update that disabled the preview pane. I believe Microsoft no longer allows document preview by default in the most recent build. This is to address a vulnerability where attackers use the preview pane as a way to steal credentials. Please see this article for more details.
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Greg Barnes 0 Reputation points
2026-03-26T09:06:17.2333333+00:00 Thanks. What is the Preview Handler and how do I see if the preview handler is correct and working?
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Q&A Assist2026-03-26T01:40:37.19+00:00 AI generated content. This question contains an answer created with AI from Q&A Assist. Learn moreIn Windows 11, File Explorer’s preview behavior depends on file type, source, and the preview/thumbnail providers that are installed.
For PDFs specifically, there are two relevant behaviors from the context:
- PowerToys File Explorer add‑ons can replace the default PDF preview handler and provide both preview‑pane and thumbnail support for PDFs. When enabled, this handler can change how PDFs appear in the preview pane (and may conflict with other handlers such as Outlook’s PDF preview):
- Open PowerToys.
- Go to File Explorer add-ons.
- For PDF under Preview Pane previewers, turn the extension On (or Off if preferring the default Windows/Adobe handler instead).
- For Thumbnail previews, also turn PDF On if wanting thumbnails generated by PowerToys.
- If changes do not take effect, restart Windows.
- For files stored in locations that use cloud or tiered storage (for example, Azure File Sync or some OneDrive scenarios), Windows may intentionally skip generating thumbnails and previews for files that are not fully local:
- With Azure File Sync and Cloud Tiering, tiered files have the offline attribute set, and Windows’ thumbnail cache intentionally does not read those files, so thumbnails and previews are not shown until the file is recalled locally.
- This is expected behavior; to see thumbnails/previews, configure the sync solution so that the offline attribute is not set, or ensure the file is fully downloaded/kept on the device.
If PDFs are only showing as small thumbnails inside the preview pane while other image types show a full preview, verify which PDF preview handler is active (PowerToys vs. another handler) and whether the PDFs are stored in a cloud/tiered location that may restrict full preview generation.
References:
- PowerToys File Explorer add‑ons can replace the default PDF preview handler and provide both preview‑pane and thumbnail support for PDFs. When enabled, this handler can change how PDFs appear in the preview pane (and may conflict with other handlers such as Outlook’s PDF preview):